1. Field of the Invention
The present invention relates to an optical PCB, a module for the optical PCB and an optical connection block, and more particularly, to an architecture of connecting an optical PCB, a transceiver modules for the optical PCB, and an optical connection block for passively aligning the optical connection block for optical coupling between the transceiver module and waveguides mounted in the optical PCB.
2. Background of the Related Art
With the development of IC (Integrated Circuit) technology and improvement of operating speed and integration scale of ICs, the performance of microprocessors and capacity of memory chips are rapidly increased. Accordingly, next-generation information communication systems constructed of large-capacity parallel computers or ATM (Asynchronous Transfer Mode) switching systems of terabit (Tb/s) grade, which transfer a vast quantity of information at a high speed, require improved signal processing capability. Accordingly, an increase in signal transmission speed and density of wires is needed.
However, conventional devices have limitations in increasing signal transmission speed and density of wires because information transfer in a short distance, such as between boards or between chips, is carried out using electric signals. Furthermore, the resistance of wires causes signal delay in the conventional devices. Moreover, an increase in signal transmission speed and wire density generates noises caused by electromagnetic interference and thus countermeasures against the noises are needed.
To solve this problem, a waveguide capable of transmitting and receiving optical signals using a polymer and a glass fiber has been recently imbedded into a PCB, which is called EOCB (Electro-Optical Circuit Board). The EOCB handles both of electric signals and optical signals and performs super high-speed data communication using optical signals in the same board. The waveguide and a glass substrate are imbedded in the PCB when a copper circuit pattern is formed such that data can be converted into electric signals to be stored/processed in a device.
Optical lines can be applied to connection of devices, connection of boards, or connection of chips. Particularly, the optical lines are suitable for constructing optical transmission communication systems for signal transmission in relatively short distance, such as between a chip and another chip.
Conventional EOCBs include a transmission silicon chip, a light-emitting unit, an optical substrate, a photo-detecting unit, and a receiving silicon chip, which are formed on a silicon substrates, and use a lens for optical coupling. However, This construction cannot be classified as an optical backplane, which is a modified form of an optical transceiver module and is applied to a general PCB to solve electrical connection problems.
An example of conventional optical backplanes is disclosed in U.S. Pat. No. 6,324,328, entitled “Circuit carrier with integrated, active, optical functions”, in which a waveguide is used as an optical line for transferring signals and placed in a PCB.
Another example is a configuration in which a surface-emitting laser and a photodiode are sealed in a hole formed in the backside of a plastic BGA package and two polymer micro-lenses are arranged on a single optical path, to extend packaging tolerance. This configuration enables parallel transmission of optical signals between IC packages and remarkably reduces packaging cost. However, this technique is difficult to use because of three alignment errors, that is, an error generated when a waveguide is placed in a PCB, an error generated when the surface-emitting laser is attached to the backside of the plastic BGA, and an error generated caused by secondary internal connection when the plastic BGA is soldered to the PCB. Furthermore, it cannot spread or cool down heat emitted from the chip because the surface-emitting laser has a completely closed structure.
An example of conventional modules for optical PCBs is U.S. Pat. No. 6,512,861. Referring to FIG. 9, a bottom emitting or sensing active photo-electric element 102 is flip-chip-bonded to a transmission or receiving chip 104 using solder bumps 120 and 122. In addition, the transmission or receiving chip 104 is also flip-chip-bonded to a BGA package substrate 108 and integrated on a printed circuit board 110 having an alignment ball placed in a V-groove 160 to facilitate the alignment of a BGA package.
Another example of the conventional modules for optical PCBs is disclosed in U.S. Pat. No. 6,396,968, in which an active photo-electric element is mounted on an electric PCB and vertically installed in the PCB such that the active photo-electric element is directly connected to an optical waveguide placed in the PCB.
In the meantime, a function of reflecting optical signals orthogonally for optical-coupling an active photo-electric element integrated in an optical PCB and a waveguide located in the optical PCB is required in optical configurations other than the configuration in which the active photo-electric element is directly connected to the optical waveguide arranged in the PCB. For this, methods of forming a mirror face in a structure in which the end of an optical waveguide or optical fiber mounted on an optical PCB is tilted at 45° are proposed, which are disclosed in U.S. Pat. No. 6,257,771 and U.S. Pat. No. 6,389,202.
Furthermore, a technique of inserting an optical connection block having a reflecting face (or reflecting system) into a groove formed in a PCB and integrating active photo-electric elements thereon to reflect lights orthogonally is used. This technique is disclosed in U.S. Pat. No. 6,285,808 and U.S. Pat. No. 6,370,292.
In the meantime, U.S. Pat. No. 6,516,105 B1, entitled “Optical backplane assembly and method of making same”, discloses a method of aligning an optical backplane on a motherboard. Referring to FIG. 10, a fluorescent material 122 reacting to UV rays is coated on an optical layer in an optical PCB. Then, UV rays 208 are irradiated to one side of the fluorescent layer 122 and light emitted from the fluorescent layer is detected by a detector 216 at the other side of the fluorescent layer, to fix an optical connection component 124 to the light-emitting position.
Furthermore, an optical connection block, as shown in FIG. 11, is constructed in such a manner that optical fibers are curved at a right angle inside a hexahedron block to transfer light input from the top surface of the block to the side of the block.
For optical coupling between chips based on an optical PCB, sufficiently high optical coupling efficiency must be maintained by aligning an optical PCB in which optical waveguides are mounted, a transceiver modules for the optical PCB in which active photo-electric elements are integrated, and an optical connection block serving as an optical signal paths between the transceiver module and the optical PCB with high accuracy. Furthermore, complete passive alignment is required because active alignment increases packaging cost. A conventional technique that mounts active photo-electric elements in through-holes of a BGA substrate and then integrates BGA packaging in a PCB using a solder ball, which is disclosed in U.S. Pat. No. 6,512,861, can passively align an optical PCB with a transceiver modules for the optical PCB according to self-alignment of the solder ball. However, this technique cannot align the optical PCB and the optical connection block or the transceiver module for the optical PCB and the optical connection blocks passively.
The method of aligning the optical backplane on the motherboard, disclosed in U.S. Pat. No. 6,516,105, detects light emitted from the fluorescent material with a detector using an active method, and then moves the optical connection block to the position of the detector. However, this technique requires a separate process to increase operating time. Furthermore, alignment of the optical connection block can be deviated while the optical connection block is moved.
Moreover, the aforementioned structure in which the optical fibers are curved at a right angle in the hexahedron block to transfer light input from the top surface of the block to the side of the block has a difficulty in passive alignment of the block with an optical PCB or a transceiver module for the optical PCB.
The above-described complicated process for overcoming alignment problems increases the manufacturing cost of optical backplane over general PCBs.